The present invention relates to farming of aquatic animals and, in particular, it concerns a food formulation for aquatic animals with integrated targeted delivery of bioactive agents.
Considerable effort has been made to develop a formulated feed for aquatic animals to replace live feed. This is due to a number of disadvantages associated with live feed such as: challenges in cultivation, variable supply due to periodic and sometimes low hatching, variable nutritional composition, risk of transferring diseases and overall cost. A suitable replacement, which would result in survival and growth rates comparable with live feed, has yet to be developed. The lack of adequate formulated feed for aquatic animals, as a substitute for live feed, is a substantial hindrance for the development of the industry of fish farming.
In addition, there is a great need in aquaculture to develop a method of mass immunization, as well as administration of growth enhancing bioactive molecules. Presently, the most effective method available to administer bioactive macromolecules, such as growth hormones or vaccines, is by injection. It is self evident that this is impractical with fish larvae. Oral administration through formulated feed is generally precluded because conventional feeds rapidly deteriorate in water with physical decomposition. Consequently, vulnerable bioactive molecules start to breakdown, and can then be destroyed before they are even subject to the biological, chemical and physical gastrointestinal tract processes.
Turning now to the field of drug delivery in mammals, polymerized, microencapsulated, and polymer-coated liposomes, as well as other lipid particulate carriers are known in the art as potential carriers via the oral route. The most important contribution of oral particulate carriers is in their ability to protect their contents until direct release in time and place, thereby maximizing efficacy. Various methods have been proposed in the prior art to achieve retention and increased absorption, including dosage forms which display extended residence along the gastrointestinal tract due to their density, size, or use of mechanisms based on pH or bioadhesion.
While cationic liposomes have been shown to adhere to the digestive tract mucosa in mammalian studies such as rat (Jubeh, T. T., et al., Pharmaceutical Research, Volume 21, Issue 3, March 2004, Pages 447-453) and human, no studies have considered its efficacy in adult and larval aquatic animals. Although the mucosa in both fish and mammals are similar, it is not self evident that liposomes in the digestive tract of fish, would adhere to the mucosa just as readily as in mammals. The membrane fatty acid composition of mammalian digestive tract mucosa and fish digestive tract mucosa can differ significantly in polyunsaturated fatty acid content. Bailey and Cullis (Biochemistry. 1997 Feb. 18;36(7):1628-34) reported that membrane fusion with cationic liposomes is markedly affected by membrane lipid composition. In addition, due to the significant difference in body temperature of mammals, being warm blooded (about 37° C.), and fish, being cold blooded, there is an anticipated adjustment in the physical-chemical properties of the liposome membrane. This would be the case whether the liposomes are made up of hydrogenated polar lipids, where the transition temperature is known to be high or of monounsaturated or polyunsaturated moiety, which have much lower transition temperatures, both studied in mammals.
Even once delivery of the molecules is achieved, the prior art compositions have generally proved deficient in inducing increased absorption by the digestive system of bioactive macromolecules.
In aquatic animals, formulated feed is added to the aquaculture system or mixed with water prior to use and begins to decompose, even before entering the digestive system of the organism. One method for overcoming some of these disadvantages has been the application of microencapsulated diets. WATHNE (PCT WO 00/27218) discloses a formulated feed for aquatic organisms which is both stable so as to prevent leakage of water soluble nutrients and easily digestible to larvae. It is able to contain both water soluble and insoluble nutrients. Harel (PCTA 04043140 (2004)) discloses a method of protection of the bioactive compounds and microbes from digestion and destruction by the digestive system of aquatic organism as well as controlled release.
However, microencapsulated feed for aquatic animals described in the prior art is limited to advances in appropriate delivery vehicles. The prior art is still deficient in providing factors which sequentially prime key elements of the digestive tract for improved efficiency in digestion, absorption, and assimilation. It will be appreciated for those well versed in the art, if a product can be provided which include these factors, thereby improving growth and health management and providing an economical and high performance alternative for live feed in commercial hatcheries.
Koven et al. (2002) (Marine Biology, Volume 140, Issue 6, June 2002, Pages 1241-1247) studied ingestion of liposomes that contained soluble proteins such as bovine serum albumin (BSA) and specific Free Amino Acids (FAA) by first feeding herring larvae (Clupea harengus). Ingestion of these liposomes was associated with stimulation of significantly higher levels of cholecystokinin (CCK), a digestive hormone acting on the gall bladder, pancreas and vagal neurons. However, it was not demonstrated that these FAA directly improve assimilation of lipids and proteins.
There is therefore a need for a food formulation for aquatic animals which would enable integrated targeted delivery of bioactive agents, and which would enhance absorption both of the nutrients and the bioactive agents of the formulation.